This invention relates generally to temperature control for computers, and more particularly to a method and apparatus for controlling a computer fan to cool a microprocessor and other resident computer components.
Integrated circuits and other electrical devices typically have rated operating temperature ranges. Within these ranges the devices behave according to specified requirements. Outside of such range the response characteristics of the circuits and devices can vary from the specified requirements. At excess temperatures, it is known for integrated circuits and other electrical devices to fail or burn out or otherwise become defective. Accordingly, it is desirable to maintain circuits and devices within operating temperature ranges.
In a computer system, continued operation of a device leads to the generation of heat. In some instances the ambient air is sufficient to provide cooling to maintain the circuit or device within the desired operating temperature range. Some circuits or components generate enough heat to require affirmative cooling from a fan. Typically, computers have included a cooling fan inside the computer case to prevent overheating caused by the normal operation of the computer.
As microprocessors have increased in speed, the amount of heat generated by the microprocessor also has increased. It is known to include a heat sink immediately adjacent to the microprocessor to absorb some of such heat. A challenge in designing computers with such microprocessors is that the heat generated by the microprocessor can adversely affect nearby components. For example, these high speed microprocessors often have larger operating temperature ranges and increased heat sink capabilities, while other components continue to be manufactured under prior requirement levels. Thus, although the microprocessor may handle an increased temperature, such increased temperature may adversely impact a nearby circuit or device. The impact is significant for notebook computers where components are often spaced more closely. The impact is heightened as such computers are being kept on for longer durations because many notebook computers are now used as primary computers. Accordingly, cooling techniques are important to the design and operation of notebook computers and other computer systems.
Many cooling techniques for a computer involve the operation and control of a cooling fan. One conventional scheme for controlling a computer's cooling fan is based on thermostat control. A temperature sensor detects the temperature at a prescribed location within a computer system. When such temperature exceeds a prescribed temperature, the cooling fan turns on. When the temperature falls below such temperature, the fan turns off. Typically once the fan turns on, there is a minimum time before the fan turns off. Such time prevents the fan from oscillating between on and off states. In such scheme there is just one speed for the fan. The turning on and off of the fan at full speed is noticeably noisy and irritating to the user.
Another conventional scheme for controlling a cooling fan for a computer is based on open-loop, series thermistor control. A thermistor is connected in series to the cooling fan. The specifications of the thermistor determine the temperature set point at which the fan turns on. As the temperature exceeds the set point the thermistor causes the power passed to the fan to increase. As a result the fan increases in speed. There are shortcomings of the series thermistor, however, as a basis for cooling computer components. First, there is a time lag between when the temperature reaches the set point temperature and when the thermistor changes its resistance to cause the fan to turn on or change speeds. As a result the set point temperature often has to be selected to be less than a desired set point so that the fan comes on before temperatures exceed maximum temperature specifications for nearby components (e.g., microprocessor, memory) or peripherals (e.g., hard drive, CD-ROM drive, battery, display controller). Another shortcoming is that the series thermistor is a large component which is too big to locate near a microprocessor--particularly for notebook computer implementations.